PROJECT SUMMARY Schizophrenia is a serious psychiatric disorder that affects up to one percent of the world's population. While it has been shown that this disease may be associated with molecular changes during neurodevelopment, the drivers of these changes remains unknown. Transcription factors (TFs) are attractive candidates for further study; they control the expression of entire networks of genes, and extensive TF-driven networks govern the development of neurons and other brain cell types. Our previous work leverages a publicly available GWAS of schizophrenia and an atlas of accessible chromatin in the brain to establish a regulome-wide association mod- el of this disease. This model uses DNAse-seq ?footprints? to determine likely binding sites of TFs and uses these sites to predict target genes. TFs with many targets associated with risk in GWAS are considered asso- ciated with risk themselves. This has allowed us to identify TFs that may be involved in the pathogenesis of schizophrenia, as well as the individual target genes of these TFs. Many of the top TFs identified in our model are known to be involved in cell-fate decisions, including a neurodevelopmental TF known as EMX1. We have independently observed increases in EMX1 binding activity in schizophrenia cases versus controls, and shown that EMX1 target expression is increased in excitatory neuron lineages. This work aims to validate our model and test the hypothesis that schizophrenia is associated with changes in a transcriptional network governed by EMX1 that pushes neural precursors towards premature differentiation into excitatory neurons. In silico ap- proaches using high-quality ATAC-seq and single cell RNA-seq datasets (Aim 1) will be used to confirm our previous findings that EMX1 shows increased binding activity and show that its binding targets are involved in the development of excitatory neurons. An embryonic stem cell-derived neural induction system (Aim 2) will be used to validate targets of EMX1 predicted by our model and demonstrate how EMX1 overexpression inter- feres with cortex formation. This aim will test the hypothesis that the overexpression of EMX1 activates a net- work of target genes that causes premature excitatory neuron formation during corticogenesis, resulting in later deficits in cortical structure and thickness. These experiments will demonstrate the utility of our model in identi- fying TF networks that mediate risk for schizophrenia, and demonstrate the role of the EMX1 network in neural cell type determination. This project is a part of a larger training plan designed to train me in the skills and techniques necessary for a career as a physician-scientist in neuropsychiatric systems biology. I will carry out this proposal under the guidance of my primary sponsor, Dr. Seth Ament, and my co-sponsor Dr. Margaret McCarthy. Dr. Ament is an expert in the systems biology of neuropsychiatric disease and has published more than 27 papers on the subject. Dr. McCarthy is a pre-eminent researcher in neurodevelopment with extensive experience training pre-doctoral students, including MD/PhD students. This mentoring team will supervise my development as a scientist and a clinician as I achieve the aims of this proposal and my broader career goals.